Many esters, and especially ethyl acetate, are synthesized on the industrial scale by using starting products of fossil origin (ethylene in the case of ethyl acetate) via multi-step methods. The global market for ethyl acetate was 2.5 million tonnes/year in 2008.
It is known to use a ruthenium-based catalyst to carry out the dehydrogenative coupling of ethanol using for example carbonylchlorohydrido[bis(2-diphenylphosphinoethypamino]ruthenium(II), of formula A, (CAS: 1295649-40-9), Trade Name: Ru-MACHO, or D (see below) (cf. M. Nielsen, H. Junge, A. Kammer and M. Beller, Angew. Chem. Int. Ed., 2012, 51, 5711-5713 and EP 2 599 544 A1) or trans-RuCl2(PPh3)[PyCH2NH(CH2)2PPh2], of formula B, (cf. D. Spasyuk and D. Gusev, Organometallics, 2012, 31, 5239-5242). These catalysts A and B however require the presence of tBuOK or EtONa in order to be active. The catalyst D requires a long reaction time and a high catalytic loading in order to obtain yields of at most 90% ester.

Another catalyst used for the same reaction is the carbonylhydrido(tetrahydroborato)[bis(2-diphenylphosphinoethyl)amino]ruthenium(II) catalyst of formula C (CAS: 1295649-41-0), Trade Name: Ru-MACHO-BH. This reaction is described in patent application WO 2012/144650 where this synthesis requires the presence of a hydrogen acceptor such as a ketone, for example 3-pentanone. In addition to dissolving the various species (catalyst and substrate), 3-pentanone acts as a hydrogen acceptor. Thus, an at least stoichiometric amount of 3-pentanone is used in the examples and the reactions described are therefore not accompanied by the release of gaseous hydrogen.

It is also known to use a ruthenium-based catalyst to carry out the dehydrogenative coupling of butanol using for example trans-RuH2(CO)[HN(C2H4PiPr2)2], of formula D, (M. Bertoli, A. Choualeb, A. J. Lough, B. Moore, D. Spasyuk and D. Gusev, Organometallics, 2011, 30, 3479-3482) or [RuH(PNN)(CO)], of formula E, (cf. J. Zhang, G. Leitus, Y. Ben-David and D. Milstein, J. Am. Chem. Soc., 2005, 127,10840-10841) in the presence of solvent and in the absence of base and hydrogen acceptor. However, these catalysts require long reaction times and high catalytic loadings in order to obtain yields of at most 90% ester.

Implementing such methods on the industrial scale, however, presents numerous disadvantages. One of these disadvantages is the need to carry out several purification steps in order to isolate the products of the reaction which makes the method significantly more complex. Another problem is the use of organic products, such as solvents, in addition to the starting products. The use of such products substantially increases the environmental impact of such syntheses, which should of course be avoided. A method has now been achieved that solves these problems and that thus offers a realistic alternative to the industrial methods for synthesizing esters using fossil resources. This method makes it possible to combine high yields with simplified synthesis and purification steps in the implementation.